SYNCHRONIZATION BETWEEN PREFRONTAL AND POSTERIOR ASSOCIATION CORTEX DURING HUMAN WORKING-MEMORY

We measured coherence between the electroencephalogram at different sc alp sites while human subjects performed delayed response tasks. The t asks required the retention of either verbalizable strings of characte rs or abstract line drawings. In both types of tasks, a significant en hancement in coherence in the theta range (4-7 Hz) was found between p refrontal and posterior electrodes during 4-s retention intervals. Dur ing 6-s perception intervals, far fewer increases in theta coherence w ere found. Also in other frequency bands, coherence increased; however , the patterns of enhancement made a relevance for working memory proc esses seem unlikely. Our results suggest that working memory involves synchronization between prefrontal and posterior association cortex by phase-locked, low frequency (4-7 Hz) brain activity.